Breast cancer is endemic in the United States, with nearly 216,000 new cases expected this year (American Cancer Society statistics). For patients undergoing mastectomy,the loss of one or both breasts can cause significant discomfort and psychosocial distress. The number of breast reconstruction operations exceeds 80,000 cases per year (American Society of Plastic Surgeons statistics). Current surgical options including autologous tissue flaps and implants, have significant problems. The use of adipose precursor cells, or preadipocytes, may represent a better solution for soft tissue reconstruction for cancer defects. We hypothesize that human preadipocytes can be seeded on microcarrier scaffolds and be injected into an animal model to produce a durable engineered soft tissue replacement. Furthermore, we speculate that the preadipocytes will differentiate into both adipocytes and elements of the new vascular systemthat perfusesthe fat tissue. The specific aims of this study are to: 1. Characterize cell surface markers of human preadipocytes using flow cytometry and assessthe variability of differentiation of cloned subpopulations. Preadipocytes will be isolated from adipose tissue of breast cancer patients for clinical relevance. 2. Evaluate the adherence, proliferation and adipogenic differentiation of human preadipocytes within macroporous collagenous beads and small intestinal submucosa (SIS) microparticles in culture. 3. Determine the ability of human preadipocytes to generate mature adipose tissue when seeded in collagen and SIS particles and injected subcutaneously into a nude mouse.